Most integrated circuit (hereafter also referred to as IC devices, IC chips, or IC boards) contain a multitude of components, such as transistors, capacitors, resistors, processors, logic gates (for example AND, OR, NAND, and NOR, etc.), and memory caches, among others. These components are placed on a substrate material and connected by a series of electrical traces (i.e., conductors). Most components receive power via a power distribution bus which is connected to one or more power supplies.
Data signals are passed between components via the traces. The route used to pass a data signal between components is referred to as a data path, or logic path. The coupling of a data signal from one trace (usually called the aggressor) and another trace (usually called the victim) is referred to as cross-talk, whereas the effect of power supplies and power buses on a data signal is referred to as noise.
Today's integrated circuits benefit from two major improvements over integrated circuits constructed a few years ago. The first improvement encompasses the integrated circuit's operating voltage. Current integrated circuits operate at lower voltages than their predecessors. Thus, systems employing today's integrated circuits consume less power than systems employing older integrated circuits, and as such are extremely beneficial for portable devices manufactures, for example. The second improvement encompasses component density. Current integrated circuits have higher component densities than their predecessors. In other words, current integrated circuits have more components packed within a given area than older integrated circuits. Higher density integrated circuits allow manufacturers either to offer smaller devices which perform the same functions as older devices, or to offer similar sized devices with additional functions.
Undesirable effects, however, have accompanied the shift to higher density, lower voltage integrated circuits. For example, noise and cross-talk have an increased effect on internal circuit path delays. Noise and cross-talk that would have barely been noticeable within older integrated circuits may render current integrated circuits inoperable.
Compounding the problems caused by noise and cross-talk is the lack of adequate testing methods to measure their effects on signal delays (among others) within the integrated circuit. For example, noise and cross-talk effects are usually frequency dependent. Thus, during manufacture, a chip may pass a low frequency functional test, but fail to properly function when placed and operated within a system at normal operating frequency.
Current testing methods can be grouped into two categories, simulation analysis methods and laboratory analysis methods. Both categories have limitations which impact their ability to detect conditions that may lead to integrated circuit failures.
Simulation analysis methods are said to be static-based, meaning that the amount of noise is calculated from an assumption of what is actually happening within the integrated circuit. The assumptions are based on the logic topology of the integrated circuit being tested, and are not, an actual measurement of the amount of noise found on the integrated circuit. Because assumptions must be made, simulation analysis methods are inaccurate.
Some simulation analysis methods attempt to overcome this inherent inaccuracy by employing simulation vectors to determine the effects of noise and cross-talk. However, the use of simulation vectors to accurately model a device working in a system environment consumes a great amount of time. The more complex the integrated circuit, the greater the time required for testing. Simulation analysis methods, therefore, are unlikely to be used to test today's high density integrated circuits. Thus, the operating conditions which lead to circuit failures on today's integrated circuits are not discovered.
Laboratory analysis methods, the second testing category, are said to be dynamic because the chip is tested as close to its normal operating frequency as possible. Laboratory analysis methods are preferable to simulation analysis methods because the “real life” integrated circuit characteristics are more accurately modeled.
A laboratory testing method usually entails using high speed test equipment to supply vectors to the integrated circuit. Logic testers are then used to determine the effects of the vectors on the integrated circuit. Unfortunately, high speed test equipment is usually not capable of driving large numbers of vectors into the many signal pins present on the integrated circuit. Furthermore, the logic testers tend to operate at frequencies that are much lower than the operating frequency of the integrated circuit. Thus, even though preferable, laboratory analysis methods are usually avoided because it is difficult to drive a large integrated circuit at its system operating frequency while simultaneously gathering in-circuit measurements.
A need exists, therefore, for an apparatus and method for dynamically determining the effects of signal noise and cross-talk on on-chip signal propagation while the integrated circuit is operating in its normal mode. Furthermore, a need exists for an apparatus and method that allows the determination to be made quickly and using standard laboratory test equipment.